Automatic compression release



/NvL-wroe Fie/was 5 [5f-Y ll 7//////,\"/// l Jan. 9, 1968 F. B. EsTYAUTOMATIC COMPRESSION RELEASE Filed Feb. 9. 1966 United States Patent O3,362,390 AUTOMATIC COMPRESSION RELEASE Francis B. Esty, Brookfield,Wis., assignor to Wisconsin Motor Corporation, Milwaukee, Wis., acorporation of Wisconsin Filed Feb. 9, 1966, Ser. No. 526,275 11 Claims.(Cl. 123--182) ABSTRACT OF THE DISCLOSURE This disclosure relates to anautomatic compression release for an internal combustion engine havingan exhaust valve with a valve lifter and cam mechanism for actuating thevalve lifter. The compression release includes a latch rotor pin havinga bearing seat in the cam shaft and on which the pin may turn on itslongitudinal axis, and a latch rotor pin turning mechanism responsive toengine speed to selectively rotate the pin and an eccentric part on theend of the pin above and below the cam. The eccentric part is above thecam so as to engage the valve lifter when the rotor pin is one positionat low engine speeds and is below the cam so as not to engage the valvelifter at high engine speeds.

This invention relates to an improved automatic compression release foran internal combustion engine.

It is well known in the art to provide mechanism to hold the exhaustvalve in the cylinder head of an internal combustion engine slightlyopen during the compression stroke thereof, thus to partially relievethe compression in the cylinder during starting so that starting torquerequirements of the engine are greatly reduced. When the engine startsand comes up to running speed, the compression release mechanism isrendered ineffective to permit the exhaust valve to close, thus toachieve full power of the engine at running speeds. Such a mechanismalso eliminates the need for a spark retarding mechanism, as thecompression release prevents kickback during starting.

An early example of such an automatic compression release mechanismwhich automatically responds to engine speed changes under the controlof a centrifugally responsive ilyweight is shown in British Patent28,286 of A.D. 1912. The improvement of the present invention alsorelates to a centrifugally controlled automatic compression releasemechanism. The structure of the present invention `is greatly simplifiedover that shown in the British patent aforesaid and is'adapted toreadily be added to conventional internal combustion engines withoutsubstantial modification in the engine structure. The mechanism of thepresent invention is accordingly simple, lbut will achieve all of theadvantages of an automatic compression release without materially addingto the cost of the engine.

In internal combustion engines provided with the automatic compressionrelease of the present invention, the pressure in the cylinder headduring starting is reduced to about one-half its value during running. Atypical reduction is from about 110 p.s.i. to about 60 p.s.i. Themechanism is typically effective to partially relieve compression atengine seeds below about 650 r.p.m. At speeds in excess of 650 r.p.m.,the compression release mechanism is automatically renderedinoperativeso that the exhaust valve closes under control of its timingcam on the cam shaft, thus to achieve full power at running speeds ofthe engine.

Other objects, features, and advantages of the invention will appearfrom the following disclosure in which:

FIG. `1 is a fragmentary'cross section taken through an automaticcompression release mechanism embodying the invention, shown inoperative relationship with the internal combusion engine exhaust valveand associated parts at the point in the cycle when the exhaust valveshould normally :be closed, but in which it is held slightly open by thecompression release mechanism.

FIG. 2 is a fragmentary end View taken along the line 2 2 of FIG. 1,showing the position of 'the parts at standstill or low starting speedof the engine.

FIG. 3 is a view similar to that shown in FIG. 2, but showing theposition of the parts during high running speeds of the engine.

FIG, 4 is a perspective view of the flyweight and latch pin, shown inspaced apart relationship.

FIG. 5 is a cross section taken along the line 5-5 of FIG. l, when theengine is at standstill or turning slowly, as also shown in FIG. 2,

FIG. 6 is a cross section similar to FIG. 5, but showing the position ofthe parts when the engine is at running speeds, as is also shown in FIG.3.

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention which may be embodied inother specific structure. The scope of the invention is defined in theclaims appended hereto.

Cylinder head 10 of a four-stroke internal combustion engine istypically provided with a combustion chamber 11 in which there is anexhaust valve 12 which controls flow of gases through the duct 13 to theexhaust manifold 14. Valve 12 has a stem 15 which is actuated by a valvelifter including a tapper or pad 16. Tapper 16 normally follows thecontour of cam 17 on cam shaft 18 under the influence of spring 22. Asis conventional, cam shaft 18 is driven in the direction of arrow 45 bythe engine crankshaft having pinion 19 which meshes with gear 33 on camshaft 18. Accordingly, the operation of valve 12 is timed by the cam 17,

Cam 17 has a low profile lobe or base circle section 21 Which ordinarilypermits the valve 12 to be closed during the compression stroke of thepiston in the cylinder. The valve will close under pressure of thespring 22 which bears on the stern collar 23. During the exhaust strokeof the piston in the cylinder, the high lobe 24 of the cam 17 opens thevalve 12 widely, to exhaust spent gases.

The compression release mechanism of the invention is mounted on thegear 33, which functions as a mounting plate for various parts of therelease mechanism. A bearing opening 32 is provided in gear or plate 33for a latch rotor in the form of a latching pin 25. The main body ofrotor or pin 25 is cylindrical and ts into an elongated bearing seat orsaddle 26 formed in the periphery of shaft 18, at one side of the cam17. Saddle 26 is elongated on an axis parallel to the axis of shaft 18.At its end 27 which is adjacent cam 17, and beneath the valve lifter pad16, pin 25 has a flat or relieved portion 28. This makes the outerperiphery of part 27 eccentric to the axis of pin rotation. The pin 25is rotatable on its longitudinal axis, between one position in which itsend portion 27 lies below the profile of cam lobe 21, as shown in FIG.y6, and another position in which it extends above the profile of camlobe 21, as shown in FIG. 5. The rotor or pin 25 is rocked in its seat26 by applying pressure to a crank arm or lug 31, with which the otherend of the pin is provided.

Mounting plate 33 has its outer peripheryV provided with the gear teeth35 by which the cam shaft 18 is rotated by pinion 19. Accordingly, themounting plate 33, pin 25, and cam 17 all rotate in unison with the camshaft 18. All these parts maintain their same relative positions in allpositions of the cam shaft, except that the pin 25 may be rocked orrotated in its seat 26 in accordance with the position of a flyweight36, which is centrifugally responsive to engine speed.

Flyweight 36 is mounted on plate 33 by a pintle 37 extending through abearing opening 38 near one end of the yweight. Near its other end, theflyweight is prvided with a slot i1 about a stop pin 42 which is fast tothe plate 33. Pin 42 limits movement of the weight 36 about the pintle37.

Weight 36 is also provided with a socket 43 into which the lug or tooth31 of the pin 25 is received, as shown in FIGS. 2 and 3. Socket 43 islarger than the tooth 31 of pin 25 and is bounded by lingers 50, SI1which bear on opposite sides of tooth 31. Accordingly, pivotal movementof the flyweight 36 about its pintle 37 will be transmitted to the crankarm or tooth 31 on the pin 215, thus to rotate the pin on itslongitudinal axis and hence change the position o2 the flat 28 at end 27of the pin, as shown in FIGS. 5 and 6. The ilyweight is biased radiallyinwardly toward its FIG. 2 position under pressure of a clock spring 44.

The relationship between the tooth 31 to the lingers 50, 51 boundingcavity 43 is such that relatively slight pivotal movement of the weight36 will produce considerably greater pivotal movement of the pin 25. Ina practical embodiment of the invention, for a pivotal movement of theweight of about 30, pin 25 will roll 65. This is because the distancebetween the axis of pintle 37 and the points of contact of ngers 50, 51with the sides of tooth 31 is greater than the distance between saidpoints and the axis of pin 295 and because lingers 50, 51 may slidealong the sides of tooth 31 as the weight 36 swings on its pintle 37.Accordingly, the parts 43, S0, 51 and 311 constitute a motionmultiplying drive coupling between the yweight 36 and pin 25.

At standstill and during initial starting cranking of the engine, theparts will be in -their positions shown in FIGS. 1, 2 and 5. The end 27of latch pin rotor 25 will extend above the cam lobe 231 on cam 17, thusto intervene between the valve lifter `tapper 16 and the cam and holdthe exhaust valve 12 slightly open. Accordingly, the engine will turnover easily because a substantial part of the compression in the headwill be relieved through the partially open valve 12. In a practicalembodiment of the invention, the pressure in chamber 111 is thus reducedfrom 110 p.s.i. to 60 p.s.i.

After the rst tiring stroke of the engine, the engine will rapidly buildup speed. After the engine speed exceeds a certain predetermined value,for example, about 650 r.p.m., the centrifugal forces applied to theflyweight 36 are such that the flyweight will swing radially out- Wardlyabout its pintle 3-7 to impose turning torque on the lug 31 of pin 215.This will roll the pin to its position shown in FIG. 6 where its end 27beneath the flat 218 is below the level of the cam lobe 2i1. In thisposition normal cam-valve action is restored. Thereafter, the cam 17controls the position of the valve 12 and full engine power is restored.

As is clear from FIGS. 2 and 3, the respective axes of shaft 18, pin 25,and pintle 37 are radially aligned. Moreover, the ilyweight 36 isasymmetrically disposed on the mounting plate 33. The major portion ofthe flyweight 36 is ahead of the pintle with respect to its direction 0frotation, as indicated by arrow 45. Thus inertia of the rotatingiiyweight aids centrifugal force in swinging it ont against the bia-s ofspring 44.

An important relationship of the parts is that the cam shaft 18 providesa solid abutment to support the latch pin rotor 2S in its FIG. 5position, in which it holds the valve 12 Iin slightly open position.There is direct support bearing contact between the valve tapper 16, pin25, and the shaft 18, thus to oppose the bias of spring 22.

.The prole of the cam iiat 2S can be varied for timing the compressionrelease period with respect to the overall cycle of the engine. This maybe calculated for each specific engine for optimum results.

I claim:

1. `In an internal combustion engine having an exhaust valve, an exhaustvalve lifter, a cam shaft and cam to engage the valve lifter and openthe valve, and latching mechanism to engage the valve lifter to hold thevalve open when the cam would otherwise allow it to close, theimprovement in said latching mechanism comprising:

a latch rotor adjacent said cam and valve lifter,

latch rotor turning mechanism responsive to engine speed,

said latch rotor comprising a pin lfor which the cam shaft has a bearingseat in which the pin may turn on its longitudinal axis, said pin havinga part eccentric to its axis of rotation to extend above the cam toengage said valve lifter when the rotor pin is turned to one position inresponse to low engine speed and which is below the cam so as not toengage the valve lifter when the rotor pin is turned to another positionin response to high engine speed.

2. yIn an internal combustion engine having an exhaust valve, an exhaustvalve litter, a cam shaft and cam to engage the valve lifter and openthe valve, and latching mechanism to engage the valve lifter to hold thevalve open when the cam would otherwise allow it to close, theimprovement in said latching mechanism comprising a latch rotor adjacentsaid cam and valve lifter, latch ro'tor turning mechanism responsive toengine speed, said latch rotor having a part eccentric to its axis ofrotation to extend above the cam to engage said valve lifter when therotor is turned to one position in response to low engine speed andwhich is below the cam so as not to engage the valve lifter when therotor is turned to another position in response to high engine speed,said latch rotor comprising a pin, said cam shaft having a bearing seatfor the pin in which the pin may turn on its longitudinal axis, one endof Ithe pin being disposed adjacent the cam and valve lifter and havingsaid part thereon, the other end of the pin having a crank arm by whichturning movement is imparted to the pin.

3. The improvement of claim 2 in which said latch rotor turningmechanism comprises a centrifugal weight driven by the engine and aconnection between said weight and crank arm by which the pin will beturned by the weight in response to engine speed.

4. The improvement of claim 3 in which said cam shaft has a mountingplate thereon, said plate having a pintle on which the weight ismounted.

`5. lThe improvement of claim 4 in combination with a spring biasingsaid Weight radially inwardly to oppose centrifugal force.

6. '[he improvement of claim 3 in which the respective axes of the camshaft, pin, and pintle are radially aligned.

7. An automatic compression release mechanism for an internal combustionengine which has a cylinder head, an exhaust Valve in the cylinder head,a valve lifter with a spring biasing the valve toward closed position, acam shaft and cam to engage the valve lifter and open the valve, saidautomatic compression release mechanism comprising an elongated latchpin for which said cam shaft has a bearing seat parallel to itslongitudinal axis, said pin being rotatable in said seat and having oneend thereof adjacent the cam, said end having a portion eccentric to itsaxis of rotation and which will extend above the cam to engage the valvelifter when the latch pin is turned to one position in response to lowengine speed and which will be below the cam so as not to engage thevalve lifter when the rotor is turned to another position in response tohigh engine speed, said bearing seat in the cam shaft providing apositive abutment for the pin to hold the valve open against the bias ofthe valve lifter closing spring when the pin is turned to said oneposition, and latch pin turning mechanism responsive to engine speed.

8. The automatic compression release mechanism of claim 7 in which saidlatch pin turning mechanism comprises a centrifugal weight, a mountingplate for the weight, said plate being connected to the cam shaft, apintle between the weight and mounting plate whereby rotation of the camshaft and the mounting plate will transmit centrifugal force to theweight to turn it about its pintle, sa-id latch pin having a crank armin motion transmitting connection with said weight whereby the Weightwill turn the pin in its bearing seat in response to speed changes inthe cam shaft.

9. The automatic compression release mechanism of claim 8 in which therespective axes of the cam shaft, latch pin, and pintle are radiallyaligned. 4

10. The automatic compression release mechanism of 10 claim 8 in whichthe Weight has a spring -olpposing centrifugal force and biasing theWeight radially inwardly, said 5 nection comprises a motion multiplyingdrive coupling.

References Cited UNITED STATES PATENTS 3,314,408 4/1967 Fenton 12B-182RALPH D. BLAKESLEE, Primary Examiner.

